FIG. 1 shows a cross-section through a portion of a turbine engine 10. The turbine engine 10 can generally include a compressor section 12, a combustor section 14 and a turbine section 16. A centrally disposed rotor 18 can extend through the three sections.
The turbine section 16 can include alternating rows of stationary airfoils 20 (commonly referred to as vanes) and rotating airfoils 22 (commonly referred to as blades). Each row of blades can include a plurality of airfoils 22 attached to a disc 24 provided on the rotor 18. The rotor 18 can include a plurality of axially-spaced discs 24. The blades 22 can extend radially outward from the discs 24.
Each row of vanes can be formed by attaching a plurality of airfoils 20 to the stationary support structure in the turbine section 16. For instance, the airfoils 20 can be hosted by a vane carrier 26 that is attached to the outer casing 28. The vanes 20 can extend radially inward from the vane carrier 26 or other stationary support structure to which they are attached and terminate in a region referred to as the vane tip 30.
In operation, the compressor section 12 can induct ambient air and can compress it. The compressed air 32 from the compressor section 12 can enter a chamber 34 enclosing the combustor section 12. The compressed air 32 can then be distributed to each of the combustors 36 (only one of which is shown). In each combustor 36, the compressed air 32 can be mixed with the fuel. The air-fuel mixture can be burned to form a hot working gas 38. The hot gas 38 can be routed to the turbine section 16: As it travels through the rows of vanes 20 and blades 22, the gas 38 can expand and generate power that can drive the rotor 18. The expanded gas 40 can then be exhausted from the turbine 16.
However, there are a number of places in which leakage of the gas 38 can occur in the turbine section 16. Such leakage can result in measurable engine performance decreases in power and efficiency. One area in which such leakage can occur is at interface 41 between the vanes 20 and the neighboring rotating structure. One known system for minimizing such leakage is by the use of a brush seal. An example of a known brush seal system is shown in FIG. 2. One or more brush seals 42 can be operatively attached to the vane 20, such as by a seal housing 44 attached to the vane 20 in the tip region 30. The seals 42 can extend radially inward from the seal housing 44. The seals 42 can be in close proximity to the neighboring rotating components, such as axial extensions 46 provided on the discs 24. A clearance C can be defined between the brush seals 42 and the disc extensions 46.
However, the rotating and stationary components of the turbine section 16 radially expand and contract at different rates when the engine is operating under transient conditions. For instance, when the engine is restarted soon after shutdown, which is sometimes referred to as a hot restart, the rotating components can grow radially outward at a faster rate than the stationary components. This differential in radial growth can be attributed to the faster thermal response of the rotating components and to the centrifugal forces acting on the rotating components. As a result, the clearance C can reduce to zero or less, and the brush seals 42 can rub against the disc extensions 46. Though the brush seals 42 can withstand such rubbing contact, extensive wearing of the brush seals 42 can occur such that the brush seals 42 become shorter. Consequently, the clearance C may become overly large when the engine reaches steady state operation, which, in turn, can have a detrimental effect on engine performance. Further, the brush seals 42 may require more frequent outages for service and/or replacement, thereby introducing significant costs over the life of the engine. Thus, there is a need for a system that can minimize such concerns.